Surface-modified silver nanocubes and a dispersion thereof in an organic solvent, and a method for producing surface-modified silver nanocubes.

Abstract

The present invention aims to provide surface-modified silver nanocubes with controlled particle size that can be dispersed in an organic solvent. [Solution] The present invention relates to a surface-modified silver nanocube comprising a metal nanocluster and silver covering the metal nanocluster, wherein a hydrophobic thiol is coordinately modified on the surface of the silver.

Description

[Technical Field]

[0001] The present invention relates to surface-modified silver nanocubes, a dispersion obtained by dispersing them in an organic solvent, and a method for producing surface-modified silver nanocubes. [Background technology]

[0002] Precious metal nanoparticles have attracted attention as optical element materials in recent years because they possess unique optical properties due to plasmons localized on the particle surface. Furthermore, since the optical properties of precious metal nanoparticles are greatly influenced by the particle size and shape, various manufacturing methods aimed at controlling these factors have been reported.

[0003] For example, Patent Document 1 discloses silver-shelled gold nanorods and silver-shelled gold nanoparticles obtained by uniformly depositing silver on the surface of gold nanorods or gold nanoparticles by reducing an inorganic silver salt in the presence of chloride ions. Patent Document 2 also discloses a method for producing single-crystal silver nanospheres containing gold nanoseeds based on aqueous phase synthesis. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2009 / 096569 [Patent Document 2] Chinese Patent No. 108723385 Specification [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the gold core-silver shell nanoparticles described in Patent Documents 1 and 2, gold particles with a particle size on the order of 10 nm to 100 nm are used as the core, resulting in relatively large particle sizes for the resulting gold core-silver shell nanoparticles. Furthermore, the gold core-silver shell nanoparticles described in Patent Documents 1 and 2 are manufactured in an aqueous system and cannot be dispersed in an organic solvent.

[0006] Therefore, the present invention aims to provide surface-modified silver nanocubes that have a controlled particle size and can be dispersed in an organic solvent. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have found that the above problems can be solved by a surface-modified silver nanocube comprising a metal nanocluster and silver covering the metal nanocluster, wherein hydrophobic thiols are coordinately modified on the surface of the silver, and have completed the present invention.

[0008] In other words, the present invention is as follows. 1. comprising metal nanoclusters and silver covering the metal nanoclusters, A surface-modified silver nanocube, wherein a hydrophobic thiol is coordinately modified on the surface of the silver. 2. The surface-modified silver nanocube according to 1., wherein the hydrophobic thiol is at least one compound selected from the group consisting of thiol-containing aliphatic hydrocarbon compounds, thiol-containing aromatic hydrocarbon compounds, and thiol-containing heterocyclic compounds, and at least one hydrogen atom bonded to the carbon atom of these compounds may be substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups. 3. The surface-modified silver nanocube according to 1., wherein the metal nanocluster is a gold nanocluster. 4. The surface-modified silver nanocube according to 1., wherein the length of one side excluding the hydrophobic thiol that coordinates to the surface of the silver is 20 to 35 nm.

[0009] 5. A dispersion liquid obtained by dispersing the surface-modified silver nanocubes according to any one of 1. to 4. in an organic solvent. 6. The dispersion liquid according to 5., wherein the organic solvent is at least one selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and heterocyclic solvents, and at least one of the hydrogen atoms bonded to the carbon atoms of these solvents may be substituted by a halogen atom.

[0010] 7. A step of adding a solution containing the hydrophobic thiol and a reaction solvent to a dispersion liquid in which silver nanocubes are dispersed in an aqueous solution containing a hydrophilic thiol and water, A step of further adding an acid and stirring to obtain a mixed liquid, and, A step of allowing the mixed liquid to stand in this order, The silver nanocubes include the metal nanoclusters and silver covering the metal nanoclusters, However, the reaction solvent is immiscible with water. A method for producing the surface-modified silver nanocubes according to any one of 1. to 4. 8. The hydrophilic thiol is at least one selected from the group consisting of thiol group-containing aliphatic hydrocarbon compounds, thiol group-containing aromatic hydrocarbon compounds, and thiol group-containing heterocyclic compounds, These compounds have a methylene group, and at least one of the methylene groups is substituted by an ether group. The production method according to 7. 9. The production method according to 7., wherein the molecular weight of the hydrophilic thiol is 300 to 50,000.

Advantages of the Invention

[0011] The surface-modified silver nanocubes of the present disclosure have a controlled particle size and can be dispersed in an organic solvent.

Brief Description of the Drawings

[0012] [Figure 1]Figure 1 shows the relationship between the absorption spectrum of a surface-modified silver nanocube according to one embodiment of the present invention and the amount of gold clusters added during manufacturing. [Figure 2-1] Figure 2-1 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 2-2] Figure 2-2 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 2-3] Figure 2-3 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 2-4] Figure 2-4 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 3] Figure 3 shows the relationship between the absorption spectrum of a surface-modified silver nanocube according to one embodiment of the present invention and the amount of silver nitrate added during manufacturing. [Figure 4-1] Figure 4-1 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 4-2] Figure 4-2 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 4-3] Figure 4-3 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Figure 4-4] Figure 4-4 shows the results of observing a surface-modified silver nanocube of one embodiment of the present invention using a scanning electron microscope. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below based on embodiments, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention.

[0014] In this specification, the "~" symbol indicating a numerical range is used to mean that the numbers before and after it are included as the lower and upper limits, respectively.

[0015] <Surface-modified silver nanocubes> The surface-modified silver nanocube of this embodiment comprises a metal nanocluster and silver covering the metal nanocluster, wherein a hydrophobic thiol is coordinately modified on the surface of the silver. In this specification, a surface-modified silver nanocube that does not have coordination modifications such as hydrophobic thiols on the silver surface is also simply referred to as a "silver nanocube".

[0016] In surface-modified silver nanocubes, "nano" means that both the long axis and short axis of the nanocube are on the order of nanometers, i.e., 1 nm or more and less than 1 μm (less than 1000 nm). Furthermore, in surface-modified silver nanocubes, "cube" means a non-spherical particle that is observed to have a square or nearly square rectangular shape under an electron microscope, and the ratio of the length of the long side to the short side of the observed square or rectangle is between 1 / 1 and 2 / 1.

[0017] In this embodiment, the length of one side of the surface-modified silver nanocube, excluding the hydrophobic thiol coordinated to the silver surface, is preferably 35 nm or less, more preferably 30 nm or less, and even more preferably 25 nm or less. On the other hand, the shorter the length of one side of the surface-modified silver nanocube, excluding the hydrophobic thiol coordinated to the silver surface, the better. There is no particular lower limit, but it can be, for example, 20 nm, 15 nm, or 10 nm. In a preferred embodiment, the length of one side of the surface-modified silver nanocube, excluding the hydrophobic thiol coordinated to the silver surface, can be, for example, 20 to 35 nm. By making the length of one side of the surface-modified silver nanocube, excluding the hydrophobic thiol that coordinates to the silver surface, 35 nm or less, the dispersibility of the surface-modified silver nanocube in organic solvents is improved, spontaneous sedimentation is less likely to occur, and the handling of the dispersion, described later, is improved, which is preferable.

[0018] The length of one side of a surface-modified silver nanocube, excluding the hydrophobic thiols that coordinate to the silver surface, can also be considered the length of one side of the silver nanocube. This length can be determined as the average of the side lengths of the silver nanocube portion of 50 surface-modified silver nanocubes randomly selected from scanning electron microscope (SEM) images.

[0019] [Metal nanoclusters] The surface-modified silver nanocubes of this embodiment include metal nanoclusters. In this specification, "metal nanocluster" refers to a minute particle composed of metal atoms, with a diameter typically of a few nanometers or less.

[0020] Metal nanoclusters are the core particles of surface-modified silver nanocubes, and they play a role in controlling the particle size of the silver nanocubes that make up the surface-modified silver nanocubes, as well as in making the particle size uniform.

[0021] There are no particular restrictions on the metal atoms that make up the metal nanoclusters, as long as they can form nanoclusters, but gold, silver, platinum, ruthenium, palladium, iridium, osmium, rhodium, or copper are preferred, and gold is more preferred.

[0022] For metal nanoclusters to effectively perform the roles described above, an average particle size of 1-2 nm is generally preferred.

[0023] In this specification, "average particle diameter" is determined by measuring the Ferret diameter of 50 particles randomly selected from scanning electron microscope (SEM) images and averaging them.

[0024] Furthermore, it is preferable that the aspect ratio of the metal nanoclusters is 1, that is, that the metal nanoclusters are perfectly spherical, but the aspect ratio may be greater than or equal to 1. It is also preferable that it is 2 or less, more preferably 1.5 or less, and even more preferably 1.2 or less. In a preferred embodiment, the aspect ratio of the metal nanoclusters can be 1 to 2.

[0025] In this specification, "aspect ratio of a metal nanocluster" means the ratio of the long axis to the short axis of the nanocluster [long axis / short axis].

[0026] In this embodiment, it is preferable that each surface-modified silver nanocube contains one metal nanocluster, but it may also contain one or more.

[0027] (Gold nanoclusters) The surface-modified silver nanocubes of this embodiment preferably contain gold nanoclusters. In other words, the metal nanoclusters are preferably gold nanoclusters. In this specification, "gold nanocluster" refers to minute particles composed of gold atoms, with a diameter of typically a few nanometers or less, and generally preferably 1 to 2 nm.

[0028] [Silver covering metal nanoclusters] The surface-modified silver nanocubes of this embodiment contain silver covering the metal nanoclusters.

[0029] [Hydrophobic thiols] The surface-modified silver nanocubes of this embodiment are formed by the coordination modification of a hydrophobic thiol to the surface of silver. By coordinating hydrophobic thiols to the silver surface, the surface-modified silver nanocubes can be well dispersed in organic solvents without agglomerating.

[0030] The hydrophobic thiol in this embodiment is not particularly limited as long as it is hydrophobic and can be coordinated to the surface of silver. A preferred embodiment is a hydrophobic thiol that is at least one compound selected from the group consisting of thiol group-containing aliphatic hydrocarbon compounds, thiol group-containing aromatic hydrocarbon compounds, and thiol group-containing heterocyclic compounds, wherein at least one of the hydrogen atoms bonded to the carbon atoms of these compounds may be substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups.

[0031] Examples of thiol group-containing aliphatic hydrocarbon compounds that can be used as hydrophobic thiols include alkylthiols having preferably 1 to 20, more preferably 3 to 15, and even more preferably 5 to 10 carbon atoms. At least one of the hydrogen atoms bonded to the carbon atoms of these compounds may be substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups. More specific examples of thiol group-containing aliphatic hydrocarbon compounds include substituted alkanethiols such as hexanethiol, heptanethiol, octanethiol, nonanethiol, decanethiol, and dodecanethiol.

[0032] Examples of thiol group-containing aromatic hydrocarbon compounds that can be used as hydrophobic thiols include aromatic hydrocarbon thiols having preferably 6 to 20, more preferably 6 to 15, and even more preferably 6 to 12 carbon atoms. At least one of the hydrogen atoms bonded to the carbon atoms of these compounds may be substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups. More specific examples of thiol group-containing aromatic hydrocarbon compounds include substituted benzenethiols such as benzenethiol, o-, m- or p-toluenethiol, o-, m- or p-fluorobenzenethiol, o-, m- or p-chlorobenzenethiol, o-, m- or p-bromobenzenethiol, o-, m- or p-iodidebenzenethiol, 2,3-, 2,4-, 2,5-, 3,4- or 3,5-xylentiol, aminobenzenethiol, carboxybenzenethiol, and hydroxybenzenethiol; and substituted naphthalenthols such as 1-naphthalenthol and 2-naphthalenthol.

[0033] Examples of thiol-group-containing heterocyclic compounds that can be used as hydrophobic thiols include heterocyclic thiols that preferably have 6 to 20, more preferably 6 to 15, and even more preferably 6 to 12 carbon atoms, and preferably contain at least one heteroatom selected from the group consisting of nitrogen (N), oxygen (O), and sulfur (S). At least one of the hydrogen atoms bonded to the carbon atoms of these compounds may be substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups. More specific examples of thiol-containing heterocyclic compounds include substituted pyridinethiols such as pyridine-2-thiol, pyridine-3-thiol, pyridine-4-thiol, 5-methylpyridine-2-thiol, 5-methylpyridine-3-thiol, 5-methylpyridine-4-thiol, 6-methylpyridine-2-thiol, 6-methylpyridine-3-thiol, and 5-(trifluoromethyl)pyridine-2-thiol; and substituted pyrazinethiols such as pyrazine-2-thiol and 6-methoxypyrazine-2-thiol.

[0034] There are no particular restrictions on the number of thiol groups that a hydrophobic thiol may have, but 1 to 2 are preferred, and 1 is more preferred. Having only one thiol group in a hydrophobic thiol prevents a single hydrophobic thiol molecule from coordinating across multiple silver nanocubes, thus improving the dispersibility of the surface-modified silver nanocubes, which is preferable.

[0035] [Hydrophilic thiols] In addition to the hydrophobic thiols, the surface-modified silver nanocubes of this embodiment may also have hydrophilic thiols further coordinated to the silver surface. In the method for producing surface-modified silver nanocubes of this embodiment, which will be described later, hydrophilic thiols are used in a single step, so that hydrophilic thiols can remain and coordinate on the silver surface of the final surface-modified silver nanocubes.

[0036] The preferred form of the hydrophilic thiol is the same as the preferred range described for the hydrophilic thiol used in the method for producing surface-modified silver nanocubes, which will be described later.

[0037] <Dispersion> The dispersion of this embodiment is obtained by dispersing the above-mentioned surface-modified silver nanocubes in an organic solvent.

[0038] [organic solvent] The organic solvent used to disperse the surface-modified silver nanocubes is not particularly limited as long as it is a solvent capable of dispersing the surface-modified silver nanocubes. A preferred embodiment is at least one selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and heterocyclic solvents, in which at least one of the hydrogen atoms bonded to the carbon atoms of the solvent may be substituted with a halogen atom.

[0039] Specific examples of organic solvents that can be suitably used include substituted or alternatively substituted aliphatic hydrocarbon solvents such as hexane, cyclohexane, dichloromethane, dichloroethane, and chloroform; substituted or alternatively substituted aromatic hydrocarbon solvents such as benzene, toluene, and chlorobenzene; and substituted or alternatively substituted heterocyclic solvents such as tetrahydrofuran and pyridine.

[0040] The surface-modified silver nanocubes of this embodiment can be well dispersed without aggregation even when concentrated in an organic solvent, resulting in easy handling of the dispersion. In contrast, conventional silver nanocubes need to be dispersed in water, and a surfactant is required for dispersion in water, which limits the ability to increase the concentration of silver nanocubes while maintaining their dispersion in water. Furthermore, because the dispersion containing the surface-modified silver nanocubes of this embodiment has the above-mentioned characteristics, it has the advantage that, for example, when recovering the surface-modified silver nanocubes from the dispersion by centrifugation, a relatively small gravitational acceleration setting is sufficient.

[0041] [Content of surface-modified silver nanocubes in dispersion] The content of surface-modified silver nanocubes in the dispersion of this embodiment is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more. It is preferable to have a dispersion liquid containing 50% by mass or more of surface-modified silver nanocubes, as this allows for storage and transportation of the surface-modified silver nanocubes in a concentrated state.

[0042] Furthermore, the dispersion can be diluted depending on the application in which the surface-modified silver nanocubes are used, and the content of the surface-modified silver nanocubes in the dispersion can be adjusted to a desired range. For example, the content of the surface-modified silver nanocubes in the dispersion can be adjusted to 0.1% by mass, 1% by mass, or 5% by mass. In this specification, the content of surface-modified silver nanocubes in the dispersion is a value determined by the mass of silver contained in the surface-modified silver nanocubes. (Content of surface-modified silver nanocubes in the dispersion) [mass%] = (Mass of silver constituting surface-modified silver nanocubes in the dispersion) / (Mass of the dispersion) × 100 Furthermore, since the mass of silver in the mass of surface-modified silver nanocubes is dominant over the mass of metal nanoclusters and the mass of thiols coordinated to the surface, in this specification, the content of surface-modified silver nanocubes in the dispersion can be determined based on the mass of silver contained therein.

[0043] <Method for manufacturing surface-modified silver nanocubes> In one embodiment, the surface-modified silver nanocubes of this embodiment can be manufactured by a method comprising the steps of adding a solution containing hydrophobic thiol and a reaction solvent to a dispersion of silver nanocubes dispersed in an aqueous solution containing hydrophilic thiol and water (hereinafter also referred to as "step A"), further adding an acid and stirring to obtain a mixed solution (hereinafter also referred to as "step B"), and allowing the mixed solution to stand (hereinafter also referred to as "step C"), in this order. Here, the silver nanocubes contain the metal nanoclusters and silver covering the metal nanoclusters, provided that the reaction solvent is miscible with water.

[0044] [Process A] Step A in the method for producing surface-modified silver nanocubes of this embodiment is a step of adding a solution containing hydrophobic thiol and a reaction solvent to a dispersion in which silver nanocubes are dispersed in an aqueous solution containing hydrophilic thiol and water.

[0045] (Hydrophilic thiol) The hydrophilic thiol used in step A is not particularly limited as long as it is hydrophilic and can coordinate to the surface of silver. A preferred form is at least one selected from the group consisting of thiol-containing aliphatic hydrocarbon compounds, thiol-containing aromatic hydrocarbon compounds, and thiol-containing heterocyclic compounds, and these compounds include hydrophilic thiols having a methylene group, in which at least one of the methylene groups is substituted with an ether group. The hydrophilic thiol preferably has an ether bond represented as -CH2-CH2-O-.

[0046] Examples of thiol-containing aliphatic hydrocarbon compounds that can be used as hydrophilic thiols, having a methylene group and in which at least one methylene group is substituted with an ether group, include thiol-containing polyethylene glycols such as polyethylene glycol thiols and polyethylene glycol dithiols.

[0047] Examples of thiol-containing aromatic hydrocarbon compounds that can be used as hydrophilic thiols include compounds that contain at least one aromatic ring selected from the group consisting of a benzene ring, a naphthalene ring, and an anthracene ring.

[0048] Examples of thiol-containing heterocyclic compounds that can be used as hydrophilic thiols include compounds having a methylene group, in which at least one methylene group is substituted with an ether group, and which preferably contain at least one heteroatom selected from the group consisting of nitrogen (N), oxygen (O), and sulfur (S) as the heteroatom of the heterocycle.

[0049] There are no particular restrictions on the molecular weight of the hydrophilic thiol, but it is preferably 300 to 50,000, more preferably 700 to 30,000, even more preferably 1,000 to 15,000, particularly preferably 1,500 to 8,000, and most preferably 3,000 to 6,000.

[0050] There are no particular restrictions on the number of thiol groups that a hydrophilic thiol has, but 1 to 2 is preferred, and 1 is more preferred. If the hydrophilic thiol has only one thiol group, it is preferable because a single hydrophilic thiol molecule cannot coordinate across multiple silver nanocubes, improving the dispersibility of the silver nanocubes and allowing the processes from step B onward to proceed smoothly.

[0051] (Silver nanocubes) The silver nanocubes used in step A include the metal nanoclusters and silver covering the metal nanoclusters. In other words, the silver nanocubes are the surface-modified silver nanocubes of this embodiment with the hydrophobic thiols that are coordinated to the surface of the silver removed.

[0052] The preferred morphology of the metal nanoclusters contained in the silver nanocubes and the silver covering them is the same as that described for surface-modified silver nanocubes.

[0053] Silver nanocubes are obtained by reducing a silver source with a reducing agent in the presence of a protective agent, using metal nanoclusters as a nucleus. For example, they can be obtained by adding a silver nitrate (AgNO3) solution, ascorbic acid, and metal nanoclusters to a hexadecyltrimethylammonium chloride (CTAC) solution, stirring, and continuing stirring at 60°C for more than one hour. The core metal nanoclusters are obtained by reducing a metal source with a reducing agent in the presence of a protective agent. To produce gold nanoclusters, for example, a solution of hexadecyltrimethylammonium chloride (CTAC), a solution of chlorauric acid (HAuCl4), and sodium borohydride (NaBH4) are added and stirred. Stirring continues at room temperature for more than one hour, and the excess sodium borohydride is consumed to obtain gold nanoclusters.

[0054] Examples of metal sources used in the production of metal nanoclusters include, as a gold source, chloroauric acid, chloroaurate, potassium gold cyanide, gold bromide, etc.; as a silver source, silver nitrate, silver carbonate, etc.; and as a platinum source, potassium chloroplatinate, etc. Examples of reducing agents include inorganic compounds such as sodium borohydride and hydrazine, organic acids such as hydroquinone, ascorbic acid, and citric acid, or their salts.

[0055] Examples of the protective agent used for producing the metal nanoclusters include surfactants such as hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, and polyoxyethylene(20)sorbitan monolaurate, water-soluble polymers such as gelatin, bovine serum albumin (BSA), polyvinylpyrrolidone, and polydiallyldimethylammonium chloride, and organic acid-based compounds such as citric acid.

[0056] Examples of the silver source used for producing the silver nanocubes include, for example, silver nitrate, silver carbonate, etc. Examples of the reducing agent include inorganic compounds such as sodium borohydride and hydrazine, organic acids such as hydroquinone, ascorbic acid, and citric acid, or salts thereof.

[0057] When the amount of the silver source used is fixed, the amount of the metal nanoclusters used affects the size of the produced silver nanoclusters. Specifically, per mole of the silver source, it is preferable to add metal clusters corresponding to 1×10 -6 to 1×10 -13 mol of metal atoms, more preferably 1×10 -7 to 1×10 -12 mol, even more preferably 1×10 -8 to 1×10 -11 mol, and for example, it can be 2.5×10 -9 to 5×10 -11 mol. -10 When adding metal clusters corresponding to 2.5×10 or more mol of metal atoms per mole of the silver source, small silver nanocubes are generated, which is preferable. Also, when adding metal clusters corresponding to 1.25×10 -6 mol or less, large silver nanocubes are likely to be generated, which is preferable. -11 On the other hand, when the amount of the metal nanoclusters used is fixed, the amount of the silver source used affects the shape of the produced silver nanoclusters. Specifically, per 2.5×10 -10 mol of metal atoms.

[0058] When the amount of the silver source used is fixed, the amount of the metal nanoclusters used affects the size of the produced silver nanoclusters. Specifically, per mole of the silver source, it is preferable to add metal clusters corresponding to 1×10 -10Per mole of metal nanoclusters, the silver source is 2.5 × 10⁻⁶ -8 ~4×10 -6 It is preferable to add 5 × 10⁻⁶ moles. -8 ~2×10 -6 It is more preferable to add a molar, 1 × 10 -7 ~1 × 10 -6 It is even more preferable to add molars, for example, 5 × 10 -7 ~1 × 10 -6 It can be added in moles. 2.5 × 10 as metal atoms -10 The amount of silver source added per metal nanocluster equivalent to a mole is 5 × 10 -7 A concentration of 1 × 10⁻⁶ or more is preferable because it facilitates the formation of cubic silver nanocubes. -6 A value of less than one mole is preferable because it suppresses the formation of amorphous silver nanocubes.

[0059] The protective agent used in the fabrication of silver nanocubes can be the same as the one used in the fabrication of metal nanoclusters.

[0060] (reaction solvent) The reaction solvent used in step A is not particularly limited as long as it is immiscible with water. Preferred forms include at least one selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and heterocyclic solvents, in which at least one of the hydrogen atoms bonded to the carbon atoms of these solvents may be substituted with a halogen atom.

[0061] Specific examples of reaction solvents that can be suitably used include substituted or alternatively substituted aliphatic hydrocarbon solvents such as hexane, cyclohexane, dichloromethane, dichloroethane, and chloroform; substituted or alternatively substituted aromatic hydrocarbon solvents such as benzene, toluene, and chlorobenzene; and substituted or alternatively substituted heterocyclic solvents such as tetrahydrofuran and pyridine.

[0062] (Dispersion containing dispersed silver nanocubes) The dispersion in which silver nanocubes are dispersed in step A is obtained by dispersing silver nanocubes in an aqueous solution containing a hydrophilic thiol and water.

[0063] The amount of hydrophilic thiol added to the dispersion is preferably 500 to 5,000,000 moles per mole of silver nanocube, more preferably 5,000 to 500,000 moles, and even more preferably 10,000 to 100,000 moles. By setting the amount of hydrophilic thiol charged to 500 moles or more per mole of silver nanocube, the hydrophilic thiol can coordinate to the entire surface of the silver nanocube, making it less likely for the silver nanocube to aggregate in the dispersion liquid in step A, which is preferable. Alternatively, setting the amount to 5,000,000 moles or less makes it easier for hydrophobic thiol to coordinate to the surface of the silver nanocube, resulting in the surface of the silver nanocube being moderately hydrophobic, which is preferable because it makes it easier for the surface-modified silver nanocube produced in step B (described later) to migrate from water to the reaction solvent.

[0064] The amount of hydrophilic thiol added to the dispersion is preferably 0.05 to 500 mM, more preferably 0.5 to 50 mM, and even more preferably 1 to 10 mM.

[0065] The amount of silver nanocubes added to the dispersion is preferably 0.01 to 10000 nM, more preferably 0.1 to 1000 nM, and even more preferably 1 to 100 nM.

[0066] (Solution containing hydrophobic thiols and reaction solvent) The solution in step A contains a hydrophobic thiol and a reaction solvent.

[0067] The amount of hydrophobic thiol added to the above solution is preferably 1,000 to 100,000,000 moles per mole of silver nanocube, more preferably 10,000 to 10,000,000 moles, and even more preferably 100,000 to 1,000,000 moles.

[0068] Furthermore, the concentration of hydrophobic thiols in the solution is preferably 0.01 to 1000 mM, more preferably 0.1 to 100 mM, and even more preferably 1 to 10 mM.

[0069] In step A, a solution containing the hydrophobic thiol and reaction solvent is added to a dispersion in which silver nanocubes are dispersed in an aqueous solution containing a hydrophilic thiol and water.

[0070] [Process B] In the method for producing surface-modified silver nanocubes according to this embodiment, step B is a step in which an acid is further added after step A and stirred to obtain a mixed solution.

[0071] By adding acid in step B, the pH of the reaction system is adjusted, promoting the transfer of the resulting surface-modified silver nanocubes from water to the reaction solvent. There are no particular restrictions on the acid used in step B, but examples include hydrochloric acid and sulfuric acid.

[0072] There are no particular restrictions on the stirring temperature in step B, but room temperature is preferred, for example, it can be 20 to 30°C. There are also no particular restrictions on the stirring time, but 1 to 10 minutes is preferred, and 1 to 5 minutes is more preferred. The stirring in step B should be carried out in a manner that ensures the water and reaction solvent are uniformly dispersed. One example of a stirring method is stirring using a vortex mixer.

[0073] During stirring in step B, hydrophobic thiols coordinate to the surface of the silver nanocubes, and the resulting surface-modified silver nanocubes migrate from water to the reaction solvent.

[0074] [Process C] In the method for producing surface-modified silver nanocubes according to this embodiment, step C is a step of allowing the mixture obtained in step B to stand. In step C, the mixture separates into an aqueous layer and an organic layer.

[0075] There are no particular restrictions on the standing temperature in step C, but 20-30°C is preferred, and room temperature is more preferred. There are also no particular restrictions on the standing time, but 5-30 minutes is preferred, and 10-20 minutes is more preferred.

[0076] Conventional reactions that aim to modify the surface of noble metal nanoparticles using only an aqueous system without a reaction solvent have problems such as poor dispersibility of the resulting surface-modified noble metal nanoparticles, difficulty in uniformly controlling the surface modification of the noble metal nanoparticles, and poor yield of surface-modified noble metal nanoparticles. In contrast, the method for producing surface-modified silver nanocubes of this embodiment has the advantage of being able to appropriately control the surface modification of the silver nanocubes by using a reaction that transitions from water to a reaction solvent, and also has the advantage of a high yield of surface-modified silver nanocubes.

[0077] [Post-processing steps] The method for producing surface-modified silver nanocubes according to this embodiment may include a post-treatment step after step C.

[0078] As a post-processing step, for example, there is a step (hereinafter also referred to as "step D") in which the aqueous layer is removed from the system in which the aqueous layer and organic layer have been separated by step C, in order to obtain an organic layer which is a surface-modified silver nanocube-containing layer. Furthermore, a step (hereinafter also referred to as "step E") in which the surface-modified silver nanocube is recovered from the surface-modified silver nanocube-containing layer obtained in step D may also be included. In addition, known post-processing steps may be carried out as appropriate if necessary.

[0079] (Process D) Step D in the method for producing surface-modified silver nanocubes of this embodiment is an optional step in which the aqueous layer is removed from the system in which the aqueous layer and organic layer have been separated by step C, thereby obtaining an organic layer which is a surface-modified silver nanocube-containing layer.

[0080] (Process E) In the method for producing surface-modified silver nanocubes of this embodiment, step E is an optional step of replacing the solvent in the surface-modified silver nanocube-containing layer obtained in step D.

[0081] There are no particular restrictions on the method for replacing the solvent in the surface-modified silver nanocube-containing layer in step E, but for example, one step is to remove the surface-modified silver nanocube-containing organic layer obtained in step D as a supernatant using centrifugation. In step E, an organic solvent can be added to the surface-modified silver nanocube-containing layer to replace the solvent, ultimately yielding a dispersion.

[0082] <Applications of surface-modified silver nanocubes and dispersions> Generally, precious metal nanoparticles exhibit unique optical properties due to the localization of plasmons on their surface, making them suitable for use in various optical element materials. In particular, the surface-modified silver nanocubes of this embodiment can convert blue light into electrical signals due to the silver plasmons localized on their surface, and can therefore be used, for example, as photoelectric conversion materials. Furthermore, the dispersion of this embodiment can be used to stably store and transport surface-modified silver nanocubes in a concentrated state.

[0083] As explained above, the following matters are disclosed in this specification: [1] comprising a metal nanocluster and silver covering the metal nanocluster, A surface-modified silver nanocube, wherein a hydrophobic thiol is coordinately modified on the surface of the silver. [2] The hydrophobic thiol is at least one compound selected from the group consisting of thiol group-containing aliphatic hydrocarbon compounds, thiol group-containing aromatic hydrocarbon compounds, and thiol group-containing heterocyclic compounds, wherein at least one hydrogen atom bonded to the carbon atom of these compounds is substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups. The surface-modified silver nanocube according to [1]. [3] The surface-modified silver nanocube according to [1] or [2], wherein the metal nanocluster is a gold nanocluster. [4] A surface-modified silver nanocube according to any one of [1] to [3], wherein the length of one side excluding the hydrophobic thiol that coordinates to the surface of the silver is 20 to 35 nm.

[0084] A dispersion obtained by dispersing any one of the surface-modified silver nanocubes described in [5][1] to [4] in an organic solvent. [6] The dispersion according to [5], wherein the organic solvent is at least one selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents and heterocyclic solvents, and at least one hydrogen atom bonded to a carbon atom of these solvents is substituted with a halogen atom.

[0085] [7] A step of adding a solution containing the hydrophobic thiol and reaction solvent to a dispersion in which silver nanocubes are dispersed in an aqueous solution containing a hydrophilic thiol and water. Furthermore, the acid is added and stirred to obtain a mixture, and, The process includes, in this order, the step of letting the mixture stand, The silver nanocube comprises the metal nanocluster and silver covering the metal nanocluster. A method for producing surface-modified silver nanocubes according to any one of [1] to [4], wherein the reaction solvent is miscible with water. [8] The hydrophilic thiol is at least one selected from the group consisting of thiol group-containing aliphatic hydrocarbon compounds, thiol group-containing aromatic hydrocarbon compounds, and thiol group-containing heterocyclic compounds. The method for producing these compounds according to [7], wherein the compounds have a methylene group, and at least one of the methylene groups is substituted with an ether group. [9] The method for producing the hydrophilic thiol according to [7] or [8], wherein the molecular weight of the hydrophilic thiol is 300 to 50,000.

[0086] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments disclosed herein and can be implemented with appropriate modifications without altering the spirit of the invention. The embodiments disclosed herein can be implemented in various other forms, and various omissions, substitutions, and modifications are possible without departing from the spirit of the invention. [Examples]

[0087] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0088] (material) • Hexadecyltrimethylammonium chloride (CTAC): Manufactured by Fujifilm Wako Pure Chemical Corporation • Chloroauric acid aqueous solution (gold content in aqueous solution: 30.0% by mass): Manufactured by Tanaka Precious Metals Co., Ltd. • Sodium borohydride powder (NaBH4): Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. L(+)-Ascorbic Acid: Manufactured by Fujifilm Wako Pure Chemical Corporation • Silver nitrate: Manufactured by Tanaka Precious Metals Co., Ltd. • PEG-SH: Molecular weight 5,000, manufactured by Biochempeg Scientific Inc. • Octanethiol: Manufactured by Tokyo Chemical Industry Co., Ltd. Chloroform: Manufactured by Fujifilm Wako Pure Chemical Corporation • Hydrochloric acid: Manufactured by Fujifilm Wako Pure Chemical Corporation • Toluene: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0089] <Example 1> 1. Fabrication of gold nanoclusters 500 μL of CTAC (200 mM aqueous solution), 500 μL of chloroauric acid (0.5 mM aqueous solution), and 6 μL of NaBH4 (100 mM aqueous solution) were mixed. The mixture was vigorously stirred at room temperature for 2 minutes, and then allowed to stand at 30°C for 1 hour to obtain a brown dispersion of gold nanoclusters. The obtained gold nanoclusters were used in subsequent reactions in the dispersion state without isolation.

[0090] 2. Fabrication of silver nanocubes 20 μL of CTAC (500 mM aqueous solution), 100 μL of L(+)-ascorbic acid (100 mM aqueous solution), and 870 μL of ultrapure water were mixed. 0.1 μL of the gold nanocluster dispersion prepared in step 1 above was added to this mixture (silver source 1 × 10⁶). -6 2.5 × 10⁻¹⁶ gold atoms per mole -11 An amount equivalent to a mole was added and mixed. Then, 10 μL of silver nitrate (100 mM aqueous solution) was added, and the mixture was stirred at 60°C for 1 hour to obtain a dispersion of silver nanocubes.

[0091] 3. Preparation of surface-modified silver nanocubes and dispersions The dispersion of silver nanocubes obtained in step 2 above was diluted with ultrapure water to obtain an aqueous dispersion with a silver nanocube concentration of 10 nM. 40 μL of 10 mM PEG-SH aqueous solution was added to this aqueous dispersion and allowed to stand at room temperature for 15 minutes. Next, 400 μL of 10 mM octanthiol chloroform solution was added. Then, 400 μL of 1 M hydrochloric acid was added sequentially and the mixture was vigorously stirred for 2 minutes at room temperature using a vortex mixer (product name "Jenny 2", Electro Scientific Industries, Inc.). After stirring, the mixture was allowed to stand at room temperature for 15 minutes to separate the layers. The upper aqueous layer was removed by pipette to obtain a dispersion of silver nanocubes in chloroform. A chloroform dispersion was treated with a centrifuge (product name "Model 6000", Kubota Shoji Co., Ltd.) at 2000 × g for 30 minutes. After removing the supernatant chloroform layer, 400 μL of toluene was added to obtain a toluene dispersion of silver nanocubes.

[0092] 4.Analysis method (Absorption spectrum) The absorption spectra of the silver nanocubes obtained in step 2 above were measured using a spectrophotometer. The results are shown in Figure 1.

[0093] (Measurement of particle size) The surface-modified silver nanocubes prepared in Example 1 were suspended in water, dropped onto a silicon substrate in 1 μL volume, and then dried under reduced pressure to prepare a sample. More than 50 images of each sample were acquired using a JSM-7800F Prime scanning electron microscope (JEOL Ltd.), and their sizes were measured using the image processing software ImageJ (developed by the National Institutes of Health (NIH)). The obtained images are shown in Figure 2-1. In Example 1, the length of one side of the surface-modified silver nanocube, excluding the hydrophobic thiol that coordinates to the silver surface, was 38.1 ± 2.6 nm (n=50).

[0094] <Example 2> The amount of gold nanoclusters added in Example 1, step 2 was 0.5 μL (silver source 1 × 10 -6 1.25 × 10⁻¹⁵ gold atoms per mole -10 The surface-modified silver nanocubes and dispersions for Example 2 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0095] The absorption spectrum measured using the same method as in Example 1, Section 4, is shown in Figure 1. Furthermore, the particle size was measured using the same method as in 4. of Example 1. The obtained image is shown in Figure 2-2. The length of one side of the surface-modified silver nanocube prepared in Example 2, excluding the hydrophobic thiol that coordinates to the silver surface, was 27.8 ± 2.3 nm (n=50).

[0096] <Example 3> The amount of gold nanoclusters added in Example 1, step 2 was 1 μL (silver source 1 × 10 -6 2.5 × 10⁻¹⁶ gold atoms per mole -10 The surface-modified silver nanocubes and dispersions for Example 3 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0097] The absorption spectrum measured using the same method as in Example 1, Section 4, is shown in Figure 1. Furthermore, the particle size was measured using the same method as in 4. of Example 1. The obtained images are shown in Figure 2-3. The length of one side of the surface-modified silver nanocube prepared in Example 3, excluding the hydrophobic thiol that coordinates to the silver surface, was 24.0 ± 1.8 nm (n=50).

[0098] <Example 4> The amount of gold nanoclusters added in Example 1, step 2 was 2 μL (silver source 1 × 10 -6 5 × 10⁻¹⁶ gold atoms per mole -10 The surface-modified silver nanocubes and dispersions for Example 4 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0099] The absorption spectrum measured using the same method as in Example 1, Section 4, is shown in Figure 1. Furthermore, the particle size was measured using the same method as in Example 1, step 4. The obtained images are shown in Figure 2-4. The length of one side of the surface-modified silver nanocube prepared in Example 4, excluding the hydrophobic thiol that coordinates to the silver surface, was 19.6 ± 1.3 nm (n=50).

[0100] As shown in Examples 1 to 4, it was found that the greater the amount of gold nanoclusters added in Example 1, step 2, the shorter the length of one side of the surface-modified silver nanocube, excluding the hydrophobic thiols that coordinate to the silver surface, and the shorter the absorption wavelength.

[0101] <Example 5> The amount of silver nitrate added in Example 1, step 2 was 5 μL (2.5 × 10⁶ gold atoms). -10 Silver source per gold nanocluster equivalent to a mole: 5 × 10 -7 The surface-modified silver nanocubes and dispersions for Example 5 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0102] The absorption spectrum measured using the same method as in Example 1, step 4 is shown in Figure 3. The image obtained using the same method as in Example 1, step 4 is shown in Figure 4-1.

[0103] <Example 6> The amount of silver nitrate added in Example 1, step 2 was 10 μL (2.5 × 10⁶ gold atoms). -10 Silver source per gold nanocluster equivalent to a mole: 1 × 10 -6 The surface-modified silver nanocubes and dispersions of Example 6 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0104] The absorption spectrum measured using the same method as in Example 1, step 4 is shown in Figure 3. The image obtained using the same method as in Example 1, step 4 is shown in Figure 4-2.

[0105] <Example 7> The amount of silver nitrate added in Example 1, step 2 was 25 μL (2.5 × 10⁶ gold atoms). -10 Silver source per gold nanocluster equivalent to a mole: 2.5 × 10 -6 The surface-modified silver nanocubes and dispersions of Example 7 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0106] The absorption spectrum measured using the same method as in Example 1, step 4 is shown in Figure 3. The image obtained using the same method as in Example 1, step 4 is shown in Figure 4-3.

[0107] <Example 8> The amount of silver nitrate added in Example 1, step 2 was 50 μL (2.5 × 10⁶ gold atoms). -10 Silver source per gold nanocluster equivalent to a mole: 5 × 10 -6 The surface-modified silver nanocubes and dispersions of Example 8 were obtained in the same manner as in Example 1, except that the amount was equivalent to a mole.

[0108] The absorption spectrum measured using the same method as in Example 1, step 4 is shown in Figure 3. The image obtained using the same method as in Example 1, step 4 is shown in Figure 4-4.

[0109] As shown in Examples 5 to 8, it was found that the less silver nitrate added in Example 1, step 2, the more stable the particle shape of the surface-modified silver nanocubes becomes, excluding the hydrophobic thiols that coordinate to the silver surface, and the sharper the absorption peak becomes. [Industrial applicability]

[0110] The surface-modified silver nanocubes of the present invention can convert blue light into electrical signals due to silver plasmons localized on their surface, and therefore can be used, for example, as a photoelectric conversion material.

Claims

1. The material comprises a metal nanocluster and silver covering the metal nanocluster. A surface-modified silver nanocube, wherein a hydrophobic thiol is coordinately modified on the surface of the silver.

2. The surface-modified silver nanocube according to claim 1, wherein the hydrophobic thiol is at least one compound selected from the group consisting of thiol-containing aliphatic hydrocarbon compounds, thiol-containing aromatic hydrocarbon compounds, and thiol-containing heterocyclic compounds, and at least one hydrogen atom bonded to the carbon atom of these compounds may be substituted with at least one functional group selected from the group consisting of halogen atoms, amino groups, carboxyl groups, alkoxy groups, and hydroxyl groups.

3. The surface-modified silver nanocube according to claim 1, wherein the metal nanocluster is a gold nanocluster.

4. The surface-modified silver nanocube according to claim 1, wherein the length of one side excluding the hydrophobic thiol that coordinates to the surface of the silver is 20 to 35 nm.

5. A dispersion comprising surface-modified silver nanocubes according to any one of claims 1 to 4 dispersed in an organic solvent.

6. The dispersion according to claim 5, wherein the organic solvent is at least one selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and heterocyclic solvents, and at least one hydrogen atom bonded to a carbon atom of these solvents may be substituted with a halogen atom.

7. A step of adding a solution containing the hydrophobic thiol and a reaction solvent to a dispersion of silver nanocubes in an aqueous solution containing a hydrophilic thiol and water. Furthermore, the acid is added and stirred to obtain a mixture, and, The process includes, in this order, the step of letting the mixture stand, The silver nanocube comprises the metal nanocluster and silver covering the metal nanocluster. The method for producing surface-modified silver nanocubes according to any one of claims 1 to 4, wherein the reaction solvent is miscible with water.

8. The hydrophilic thiol is at least one selected from the group consisting of thiol group-containing aliphatic hydrocarbon compounds, thiol group-containing aromatic hydrocarbon compounds, and thiol group-containing heterocyclic compounds. The manufacturing method according to claim 7, wherein these compounds have a methylene group, and at least one of the methylene groups is substituted with an ether group.

9. The manufacturing method according to claim 7, wherein the molecular weight of the hydrophilic thiol is 300 to 50,000.

Images